This invention relates to refractory mixes and, more particularly it concerns a basic maintenance mix used for patching and repairing metal exit ports in steel producing vessels, such as tapholes in basic oxygen furnace (BOF) vessels, spouts in eccentric bottom tap (EBT) and off center tap (OBT) vessels, and spouts in electric arc furnaces (EAF).
Repair of a furnace taphole is usually done on a hot furnace free of molten metal. Typically, refractory sleeves are placed in the taphole. The gap between the sleeve and the taphole is variable and must be filled with a refractory material. At the cold face there is usually a 1 to 2 inch gap; at the hot face, a 6 inch gap on each side; and a 12 inch gap above the sleeve. All of the space around the sleeve is filled with a basic maintenance material. Typical downtime for changing a taphole sleeve is 5 to 7 hours. In some instances, it is not possible to repair a furnace with its molten contents emptied, but hot repairs must be done on the "run". It has been found that a maintenance mix which works well for emergency repairs to the taphole is preferred. The usual time required for emergency repairs to a taphole is about 30 minutes.
Conventional methods of filling the void between the taphole and the refractory sleeve involve gunning a magnesite-based patching mix around the sleeve. Because gunable mixes inherently have high levels of flow agents (typically water), after hardening the mixes tend to be of low density and prone to shrinking and cracking. Typically, this type of maintenance patch lasts only a few heats before further patching is required.
Creosote containing patching mixes have also been used as EAF maintenance materials. However, during heatup creosote containing mixes produce offensive fumes which create serious environmental hazards in the work place.
Patching around the sleeves is preferred simply because to replace the entire taphole block after it is worn would require shutting down the entire furnace which usually requires at least 8 to 10 hours of down time. Therefore, for reasons of economics, the industry has developed an inconvenient procedure of frequent repairing of taphole sleeves.
The need clearly exists for a longer lasting maintenance material which requires less frequent repair.